Numerous processes have already been described for granulation of metallurgical slag, wherein pressurized water or gas is used to confer hydraulic shocks on a stream of molten slag. The various techniques used in this process employ systems of inclined planes, rotating drums, and screens, followed by discharge channels or conveyor belts, etc., these systems representing a considerable investment. Moreover, it is very difficult to consistently and reproducibly obtain for a given arrangement of devices and a number of fixed parameters, an end product which has the generally desired characteristics; thus, either a majority of pellets or spherical particles is obtained, or, if the desired form is granular, the grains suffer from incomplete vitrification, excess water content, or difficulty in crushing. Finally, the majority of these known techniques require the use of very large quantities of water, often as much as 10 m.sup.3 /ton of slag, the water having the double purpose of acting as a coolant and a means of dispersing the slag.